Revert "Added isolate + thread high watermark tracking to Observatory"

runtime/observatory/lib/src/models/objects/isolate.dart

Index: runtime/observatory/lib/src/models/objects/isolate.dart
diff --git a/runtime/observatory/lib/src/models/objects/isolate.dart b/runtime/observatory/lib/src/models/objects/isolate.dart
index 8c1e3672390d3024b7d34140b5f67911f6464c20..02d436d9a8d200123b5f8f8c7534cd203c4b00bf 100644
--- a/runtime/observatory/lib/src/models/objects/isolate.dart
+++ b/runtime/observatory/lib/src/models/objects/isolate.dart
@@ -54,11 +54,6 @@ abstract class Isolate extends IsolateRef {
   /// The list of threads associated with this isolate.
   Iterable<Thread> get threads;
 
-  /// The maximum amount of memory in bytes allocated by the isolate in all
-  /// threads at a given time. Calculated using the high watermarks of each
-  /// thread alive when a thread is unscheduled.
-  int get memoryHighWatermark;
-
   /// The number of zone handles currently held by this isolate.
   int get numZoneHandles;